Magnetos are widely used as ignition spark generators in small internal combustion engines and commonly employ permanent magnets carried by a rotor as a source of magnetic flux. In many such constructions, the magneto rotor also serves as the engine flywheel and generally, one or more permanent magnets is embedded within the rim of the flywheel and each magnet is disposed between a pair of pole shoes formed of ferromagnetic material which serve to provide a suitable magnetic flux path. Prior art methods of mounting permanent magnets and pole shoes in magneto flywheel rotors include the casting of the magnet and pole shoe group directly into the flywheel body. It has also been proposed to affix the magnet and pole shoe group to the rotor by fasteners such as screws or by the use of bonding agents. In addition, preformed rotor laminates have been used which are stacked or built up about the magnet pole shoe group.
In the mass production of such magnetomotive devices, the casting of each rotor about a pole shoe magnet group usually requires the use of die inserts for properly positioning the magnet and pole shoe members within the casting. In addition, a machine finishing operation is usually needed to insure that the pole shoes will be flush with the rotor periphery. As is well recognized, such operations add significantly to the cost factor of the magnetos. It will also be appreciated that stacked rotor constructions are very costly and labor intensive. The use of fasteners and adhesives for affixing pole shoe groups onto rotors do not generally afford sufficient structural integrity and are unsuited to mass production techniques and also require periodic maintenance checks.
Accordingly, it is a principal object of the present invention to provide a magneto rotor with improved mounting of a permanent magnet and pole shoe assembly which overcomes the drawbacks of the prior art structure.
Another object of this invention is to provide a magneto construction which lends itself to automated diecasting techniques much faster and more economical than casting procedures involving the use of inserts heretofore used in fabricating magnetos.
It is yet another object of the present invention to provide a rotor construction of the above type whereby after assembly of the magnet group and rotor, machining operations are unnecessary.
It is a further object of the present invention to provide a rotor casting combined with permanent magnet and pole shoe group characterized by utmost ease of assembly, structural integrity and durability.